[Bugfix] Fix inverted condition causing thinking_token_budget to be silently ignored

[JasonKeyiL]

Summary

Fixes #41672.

Root cause: an inverted boolean condition (or not thinking_budget_tracks_reqs instead of or thinking_budget_tracks_reqs) in gpu_input_batch.py. The condition is logically backwards: it sets needs_output_token_ids = True when there are no budget-tracking requests, and fails to contribute True when there are budget-tracking requests.

In practice the bug is currently masked — self.logitsprocs_need_output_token_ids is set to True at init whenever reasoning_config is not None (introduced in the same commit), so output_token_ids is never empty and the budget works correctly end-to-end. The fix corrects the latent logical error and removes the unnecessary population of output_token_ids when no budget-tracking requests are in the batch.

Fix: remove the erroneous not (single-token change in gpu_input_batch.py).

Changes

• vllm/v1/worker/gpu_input_batch.py: remove not from or not thinking_budget_tracks_reqs
• tests/v1/logits_processors/test_correctness.py: add regression test test_thinking_budget_enforced_without_penalties that directly exercises ThinkingBudgetStateHolder with an empty vs. live output_token_ids list, verifying in_end is raised after the budget is exhausted

Test commands run

pre-commit run ruff-check --files vllm/v1/worker/gpu_input_batch.py tests/v1/logits_processors/test_correctness.py
pre-commit run ruff-format --files vllm/v1/worker/gpu_input_batch.py tests/v1/logits_processors/test_correctness.py

.venv/bin/python -m pytest tests/v1/logits_processors/test_correctness.py::test_thinking_budget_enforced_without_penalties -v
# PASSED

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[gemini-code-assist]

Code Review

This pull request fixes a bug in gpu_input_batch.py where the thinking budget was not being enforced when no penalties or bad words were set. The logic for determining if output token IDs are needed was corrected by removing an incorrect negation, ensuring the thinking budget state holder receives the necessary data. Additionally, a regression test was added to verify that the budget is correctly enforced under these conditions. I have no feedback to provide.

[JasonKeyiL]

Hi @njhill , could you please add the 'verified' label so CI can run? Thanks!

[rishitdholakia13]

Hey @JasonKeyiL , Thanks for catching this and for the fix. I was wondering: with reasoning mode on, ReasoningConfig is not None, so I’d expect self.logitsprocs_need_output_token_ids to be set, since that was verified with the E2E test as well. How did we end up with thinking_budget_tracks_reqs being set to True while self.logitsprocs_need_output_token_ids was False?

[JasonKeyiL]

Thanks for reply and follow up! @rishitdholakia13
sorry I missed it, you are right, self.logitsprocs_need_output_token_ids is already True at first whenever reasoning_config is not None, output_token_ids shouldn't be empty in practice
but isn't the or not thinking_budget_tracks_reqs logically inverted? but given it's masked, is it worth fixing or should I close this?

[rishitdholakia13]

Yes, definitely we can merge this fix.

[JasonKeyiL]

Thank you, Hi @njhill Nick, would you be able to take a look and put a verify label? thanks!

[JasonKeyiL]

@njhill looks like a globe infra issue, CI failed with pytorch-compilation-unit-tests, pytorch-fullgraph-smoke-test, 3 times, could you manually merge it when you get a chance? Thanks you!